Investigations during the past year have demonstrated that when the cytotoxicity of the cultured macrophage (CMA) has fully developed, removal of the regional lymph nodes (RLN) has no effect on the maintenance of that property. Macrophages in tumors were identified by the presence of IgG receptors and phagocytosis. No relation could be established between the percent of macrophages present in the tumor and the degree of lung metastasis. The macrophage content of tumors was determined during treatment with cyclophosphamide (CY) and C. parvum (CP). There was no evidence that tumor inhibition was associated with an increase in the macrophage content. This does not imply that the macrophage is uninvolved in the tumor effect of CY plus CP, but does suffest that it is unlikely that the effect of local or systemic CP with or without CY is mediated by an increase in macrophages in the tumor. Additional studies on the transfer of cytotoxic syngeneic lymph node cells have shown that the RLN is more effective than the non-regional lymph nodes in the transfer of specific cytotoxicity to the normal recipient. The importance of RLN to the effectiveness of treatment with intratumor CP and systemic CY was investigated. Results indicate that the removal of the RLN at the time of tumor cell inoculation does not affect the inhibition of tumor growth or increased survival. Surgical removal of the RLN in mice with established tumors has little effect on weight or cell numbers in the thymus or spleen. There is a retardation in the decrease of cells in the non-regional nodes. During the coming year the development of tumor specific cytotoxicity after transfer of sensitized syngeneic or xenogeneic lymphoid cells will be further investigated. The effect of removal of RLN by surgery or radiation on other lymphoid structures will be studied. Initial experiments on the use of sensitized RLN and/or normal lymph node cells in the treatment of tumor bearing mice, alone or in combination with chemoimmunotherapy, will be performed.